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Why are the wings of some modern gliders tadpole shaped?
Why are the wings of some modern gliders tadpole shaped, rather than teardrop shaped? An example is the Schleicher ASG 29. Or did they just add a flat plate at the trailing edge for the flaps and ailerons?

Source: flickr.com

The flaps and ailerons are "reflexed" on this glider. They have been raised to a setting above the normal zero position, above the airfoil's normal chord line. A number of flapped gliders have this feature.
Two main benefits are a reduction in pitching moment as the pressure distribution on the wing is moved forward, so less downforce work for the tail, reducing trim drag, and lower induced drag because with the trailing edge partially unloaded it has an effect like reducing wing area and moves the best L/D speed up a bit.  So overall, best glide angle is a bit better, and the speed it's achieved is a bit higher.
You use reflex for "penetration", going as flat as possible as fast as possible, for whatever reason, like getting through an area of sink in a hurry.

do airliners use this "reflexing" technique?  It seems their upper airfoil shape has been greatly flattened for high speed cruise efficiency.

I've never seen that but it's an interesting point because airliners cruise at low indicated airspeed relatively close to max L/D.  Likely it's simply not practical to make a double slotted fowler flap system typical of airliners reflex up.  You only see it on simple plain flaps.

Flapped airfoils will have a suction peak once the flap is deflected away from its zero deflection position. This means more load on the boundary layer and earlier flow separation at the same lift coefficient. In order to avoid this suction peak over a range of flap angles, the airfoil contour is optimized on the top side for a small positive deflection and on the lower side for a small negative deflection. Now you get that "tadpole" shape between those two flap deflections, but also more flap effectivity and lower drag.
This effect is increased on the upper side for negative flap deflections. They are standard on gliders in order to shift the laminar bucket of the airfoil to the actual lift coefficient. I bet the lower side contour of the wing in the photo is smooth across the flap hinge line.

You can position the flaps/ailerons on the ASG 29 not only downwards but also upwards. The flap/aileron is triangle shaped as you can (barely) see on this photo of an ASG 29 wing joint:

Basically you can reduce the lift (and therefore drag) of the wing by moving the flaps/ailerons upwards, extracting better speed from the wing.

The upward flexure of the trailing edge of the airfoil does two things:

It maintains attachment of the flow boundary layer across the airfoil surface and decreases drag.  Separation of the boundary layer would increase pressure drag and, essentially, momentum of the separated flow that is now being carried by the aircraft.  This would decrease penetration and adversely affect airspeed and lift-drag ratio.

For a sailplane within its maximum flight performance envelope, it decreases the forward pitching moment of the wing.  Nose-down pitching would increase airspeed and sink-rate, thereby requiring up-trim of the tail-plane to counter the nose-down tendency.  This up-trim also increases drag, thereby adversely affecting the lift-drag ratio. Up-trim can also be maintained by shifting the center of gravity aft by moving trim ballast aft. Nevertheless, the best flight characteristics for maximum lift-drag ratio of a high-performance sailplane are maintained through neutral trim settings producing no essential drag (an aerodynamically balanced aircraft), and a clean wing flying within its best performance range at the given altitude and airspeed (that is, wing Reynolds number and angle of attack).

Effectively the raised flap lowers the angle of attack by virtue of the variation of the chord line.
Less drag, higher speeds for, as has been said, penetration.

This answer could be significantly improved by adding a picture or diagram.


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If pitching moment creates drag, how can high and low moment airfoils have almost identical drag polars?
If pitching moment creates drag, how can high and low moment airfoils have similar drag polars?
Let's call a symmetrical airfoil like NACA0015 a low moment airfoil having no moment at an AOA of 0.
Let's call NACA 2415 a medium moment airfoil. Let's say it has a medium moment at an AOA of 0.
Let's call Eppler399 a high moment airfoil, and it has a high moment at an AOA of 0.
yet....
I understand pitching moment creates drag. While the above airfoils have vastly different moment polars at an AOA from -10 to + 10, they almost identical drag polars,at an AOA from -10 to +10.
How can this be?
See pics below

A high Cm airfoil does not mean it will be draggy by itself. However, it does mean that when combined with trim devices (e.g. tailplane, elevator, canard, elevon), the overall drag may be higher due to the trim drag component.
Since 25% MAC, about which pitching moments are generally cited, generally gives around 20% static margin for low speed aircraft, it's a rough first indication of how much trim would be required.

The absolute value of Cm does not matter much as you can add a constant moment by moving the centre of gravity (that is, choosing where to mount the wing). The difference between highest and lowest is what will have to be compensated by the elevator and thus create trim drag.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


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Looking for Polars for Liebeck LI74 with a Cl of 4.8!
Looking for Polars for Liebeck LI74 with a Cl of 4.8!!
Does anyone have any info on this foil?

Is this a homework question?

No. lol.  I actually want to build a low span biplane ultralight. Trying to model it in XFLR5 first. Copying a bit of the Zenith 701 with a cl of 3. Want short takeoff and landing, as in 50 feet or less. Re 300-600k.  It has a slat and a junkers flap, so sort of a multi element foil already.

Can someone answer with: there aren't any polars available so I can check off the answer, or is there a way to delete this question?

@Fred there is no need to delete it, it can remain open. It is hard to prove a negative, but maybe someone will provide a polar for this airfoil in the future.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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How to calculate the minimum radius of a turn at high alpha, without banking?
How to calculate the minimum radius of a turn at high alpha, without banking?
One sees the radio control guys flying their planes at 30deg AOA in a 5' circle at walking speed, without banking.
Obviously 99% of GA planes can't fly that slow, but what radius can one fly at slow speeds, , say at 20 deg AOA, 10 mph above stall, say 50mph in something like a Cessna150.......without banking?

Maybe this is nitpicking, but an aircraft stalls at a specific angle of attack regardless of the airspeed, and that angle is typically 16 degrees.

@Ben With slats, stall AOA of straight tapered wing can be increased well beyond 20 deg, approaching 30 deg

I can tell you that absolutely nobody turns an airplane that way.  Nobody.  RC airplanes operate at very low Rns, with absurd power to weight ratios, and no one's life is on the line, so they can do all sorts of things big airplanes don't.  In any case, you would have to establish a skidding turn rate for a given airplane by testing it.

They do at airshows. lol  :)

So why isn't it safe at 1.3Vs??

Re above, is a skidding turn safe?


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Did the twin engined Lazair ultralight have a throttle for each engine?
Did the twin engined Lazair ultralight have a throttle for each engine?
I know larger aircraft have dual throttles.
What about the smaller aircraft like ultralights?
It would be so much easier just to have a single throttle, much like a motorcycle throttle which splits into 2 on a 2 cylinder, 2 carb bike.

Comparison to single-engined motorcycle is wrong. Single engine has a single crankshaft, both cylinders must work together by definition. A more suitable comparison would be to have one lever to brake both wheels on a motorcycle - this one explains why you need two.

It's not a comparison, quadcopters have 4 engines, and only 1 throttle.... Cars have 4 tires, usually 2 independent brake systems, plus e-brake but just 1 pedal.

Quadrocopters have 4 throttles - operating them differentially is the only mean of controlling it. Cars don't have independent braking either, the circuits are redundant, but the driver cannot chose to brake front or rear. But both motorcycle driver requires the choice of braking in order to not flip over and plane pilot the choice of throttling malfunctioning engine down and the good one up.

Anyway, the point is that you have compared controlling 2 engines of a plane to controlling 2 cylinders of an engine. That comparison is wrong and you have successfully mislead yourself with it. The question would be better without it.

I've examined a Lazair, and actually taxied one around on the ground once, and yes there are two throttles.
Two reasons:
In any twin engine airplane you want to minimize or eliminate single-points-of-failure (especially with engines as unreliable as little 2-stroke water pump motors) and this means you want the keep each power plant completely mechanically independent all the way up to the throttle.
You need to be able to adjust power independently to synchronize motor RPM (because the wowowowowow of out of sync motors will drive you bonkers), as well as control each engine independently for starting etc.
So, a single throttle to control both engines is a very bad idea.

This image would suggest it had two throttles, located in the usual position on the pilot's left side:

What the heck? I knew the Lazair had 4 bladed props, but they are bolted on top of each other facing the same direction? Why not offset them by 90deg?!?!?!

@Fred Check this question


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Can you mount a net between 2 helicopters for search and rescue?
During situations where multiple people are in danger, I am wondering whether you can have a huge net mounted between 2 helicopters on a device with 2 arms on each helicopter, and when need to rescue, both devices would extend the arms to provide 4 points to connect a huge net, drop it down and then people in danger can just jump on it. Possible applications could be in firefighting or rescue offshore.

Compared with a hoist, the "what could go wrong" list with this idea seems pretty lengthy, between the risks of colliding helos (big fire, big updrafts, major turbulence) and the fact that if the two helos get even a little out of position, the victims get tipped or bounced off the net.

“situations where multiple people are in danger” - such as suspended in a net between two helicopters?  I wonder how many such people might decide that they didn’t need rescuing after all :-)

Could you? Well - technically, yes. For a little while anyway... Would you actually do it to enact effective rescue operations? No.
There's countless issues with the idea that would make it rather impractical, but I had fun thinking of some of the challenges.
For starters, the net would end up being rather rectangular. The short edges would be as long as the arms on the helicopters could be (which couldn't get too long before they get in the way of landing, flying, etc.), but then you'd need to be able to keep good separation between the two craft so the net would be quite long and thin. The shorter the net was between the two craft, the more responsive it would be to changes in altitude, distance, etc. between the two craft, making the ride even worse. So you'd want it to be long.
You can try this at home - grab a scarf or something similar, and try and hold it out fairly flat between your outstretched arms, with a little action man or barbie doll sitting on it, while going for a walk around the house. You'll be constantly adjusting your arms to keep it flat while in motion and it's still going to be a bouncy ride for your passenger.
The longer the net is, the more drag it will experience, further exacerbating the ride as the drag would be tugging the helicopters around. It wouldn't be very long before the net is pulled tight, at which point the weakest link will fail - the net might tear, but lets pretend it's very strong - the net would be pulled off the arms, the arms might be pulled off the helicopter, or a helicopter might be pulled out of the air.
I did have an idea to help reduce drag... once you've got your passengers on the net (I'll come back to challenges with that), you could have one or both helicopters execute a series of rolls or loops (depending on whether the arms are mounted to a side, or to the front) in order to twist the net up to reduce its surface area! This would have the added benefit of snugly securing your passengers inside the twists of the net.
As for people boarding the net - you'd have to lay it carefully on a flat, open stretch of ground or water. The helicopters would need to either land or very carefully hover, coordinating the entire time in order to not tangle or crash. At which point the person boarding the net could just go for a short jog (or swim) over to one of the helicopters, and board that instead (winched up in the case of water). I'm a bit of a daredevil so I might actually still opt for the net, but in my final seconds (which began counting already when I made that decision) I'd feel pretty guilty about likely destroying two helicopters, the lives of the pilots and crew, and their families.
But oh boy it would be one heck of a ride!

+1 for "series of rolls or loops ... to twist the net up to reduce its surface area"!


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Is there a database of aircraft 3D models that are accurately created
I was just wondering if there was such a thing as the title describes. I am trying to work on a machine learning algorithm that generates aircraft designs based on what it learns from current designs, where I think the appropriate dataset format is in 3D model form.
If there exists no such database/dataset, I think I might have to find each design plan of individual aircraft and extract as much information as I can (if that's even possible)

Have you checked out FlightGear flight simulator?

Good idea! Thank you. It seems I can download aircraft models...


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Why do most aircraft with variable incidence tailplane have the possibility to trim much more degrees for nose up than for nose down?
Probably the question will be a little bit confusing but I'll try my best to make it clear.
Due the position of the CP with respect of the AC, symmetrical airfoils don't produce pitching moments, but cambered airfoil having the CP behind the AC produce a nose down pitching moment.
If we consider now the CG effect, a CG forward the AC will cause a nose down pitching moment, an aft CG the opposite.
Most aircraft with variable incidence tailplane have the possibility to trim much more degrees for nose up than for nose down.

Airbus A330; source: airlinercafe.com
Is this mainly due to the position (and range) of the CG, delianeated during the design phase and normal flight operation?
Is the pitching moment of the wing (only), much less relevant?

I don't think I've ever seen a moveable stab with a larger range above neutral than below it.  Any examples?

@JohnK: I think the OP is trying to say that, starting from the neutral position, the stabiliser can go a lot further in the aircraft-nose-up (stabiliser-leading-edge-down) direction than in the aircraft-nose-down (stabiliser-leading-edge-up) direction.

Oops you're right I was careless reading it.  I thought he was asking why the stab travel would have different travel ranges on some airplane vs others.

You do understand that there isn't a Nose Up/Nose Down "neutral position" per se right?  It's just a range for low AOA/fast trim and high AOA/slow trim with the slow end having to account for the highest pitching moment worst case and the high end having to account for the lowest pitching moment worst case.  NU/ND just describes the pitch tendency that is apparent to the pilot when a change is made.  For the pilot, the trim control is best thought of as a "hands free" speed control dial with ND=fast(er) and NU = slow(er).

The larger nose-down range is for operations with flaps extended. The clean configuration will always operate near ground set.

The wide negative trim range is for operation with lowered flaps.
Fowler flaps shift the center of lift backwards both by adding wing area at the trailing edge and by increasing camber. Both effects require more downforce on the tail to shift the sum of all lift forces such that it remains at the center of gravity.


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Relation between weight of the aircraft and mach number
Is there any formula that relates weight of the aircraft with mach number?

Without any other parameters? There are a lot of factors that go into speed. This is kind of like asking if there is any relation between a cars weight and how fast it can go...

What makes you think there might be a relation between the two?

No, there isn't. Weight (which is a result of mass and gravity) is not related to mach number (which depends on velocity and the local speed of sound). You are comparing apples and oranges.


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After completing my A&P are you suppose to get a temporary license? After the exam my DME just gave me a copy of my airmen certificate application
I passed my exams on 17DEC2020. Currently the FAA's web site shows that I have no certificates, and shows that they are processing applicants from 25JAN2021...... what should I do?

To the close voter, what more information do you need to answer this?

I need to know where or not I should have some sort of Airmen number currently; and If I should be worried about my certs not showing up in the certificate search since they are processing airmen who graduated after me.

Have you called your FSDO?


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What is the difference between RTOP, MTOP, and MCP?
I am currently learning how to fly the SD3-60 (Shorts) Aircraft, and I am trying to gain an understanding of RTOP (reserved take off power), MTOP (max take off power), and MCP (max continuous power).  Can someone explain the difference between all three of these and which phases of flight/situations we would use these in?  Can someone also explain why we would use one over the other in certain conditions?  Thank you so much in advance!

MCP is maximum power that can be used indefinitely without shortening the life of the engine.  You might use MCP when you need all the available power during single engine cruise, to maintain an altitude for obstacle clearance, or when climbing single engine.
MTOP is normal maximum for takeoff and initial climb, with a time limit. If you exceed the time limit, you will shorten the life of the engine.
RTOP is a power reserve for special situations, like when an engine quits, where the engine goes above MTOP to save your butt.  When that happens on modern turboprops the dead engine will autofeather and the live one will automatically go into RTOP (sometimes called "power uptrim" or something similar).  If it does so it may have an impact on engine life or may require a special inspection later.


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Alternative methods to determine A-320 (Pegasus R1A) Optimal FL
320 FO looking to see if anyone knows a method to determine optimal flight level (essentially compute optimal step climb point) from the F-PLN page. I’m well aware of computing optimal S/C from the STEP ALTS page, but I remember long ago a line check airman dropping some code into the right side of the F-PLN page. Curious if anyone can find any information on this shortcut.


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Why do heavy departures wait 5-10 minutes on the runway at ZRH?
I'm frequently travelling to Zürich for business and I usually make my schedule so that I have at least an hour to do some planespotting and photographing at the ZRH airport.
Whenever I came to the airport, the runway usage was the same: RWY14 for all the landings, RWY28 for almost all the takeoffs, while RWY16 was used by heavies for takeoffs (usually the flights to Asia or to the USA). I noticed that once a heavy aircraft lines up at RWY16, it waits for some 5-10 minutes before it starts rolling (although it is already way behind its scheduled departure time). The only possible explanation that I could think of was that its engines would cause severe turbulence for the airplanes which are landing at RWY14 and that it has to wait for a significant gap between the landings.
Am I right? Or if not, does anyone know the real reason for these delays?

5-10 minutes sounds pretty extreme, are you sure you are not exaggerating?

There's only 1 taxiway for 14 and 16, and the apron looks like a crowded place, if there's no other movements due on 16 then taxiing the heavy and having them hold clears the airplane out of the way.

If you saw it only once, I think we can not predict many seldom motivations. Runway inspection? (VASAaviation had a ab ATC comunication about a fox crossing the runway)

Remember that flight schedules are gate to gate. An airplane well behind departure time might still be ahead of its expected “wheels up” time.

what you describe is called the "north concept". See here and here for more information (mostly in German).

The usual reason is, that departures from runway 16 are not allowed to climb straight ahead due to noise restrictions over downtown Zurich. Instead they need to turn left, where they cross the departure path of runway 14. So if there are arrivals on 14, no departures on 16 are cleared, as in the case of a go around on runway 14, its departure sector must remain free. I've been watching planes stuck for half an hour at the line up 16 for that reason. Imagine that waste of fuel... ZRH's runway capacity, despite having 3 runways, is thus actually lower than for a parallel 2-runway setup (think about London Heathrow e.g.).

This does not answer the question. It explains the delay, but not why the aircraft waits on the runway for so long. (In the USA, our rule book says that line-up-and-wait should only be used when an aircraft will be an "imminent" departure, and the guidance is that that means approximately 90 seconds.)

I don't know, but I have what I think is a reasonable guess.
First, if separation (wake turbulence mitigation) was the reason, then why would ATC block a perfectly servicable runway by having an aircraft line up and just sit there for upwards of 10 minutes? It would make far more sense to have the aircraft taxi and hold short of the runway, than to line up and wait, until there is a likely large enough gap in the traffic. Even if the first aircraft is holding short at the threshold of 16, unable to take off due to say separation concerns, it would still be possible to allow another aircraft to enter the runway from the next taxiway down, backtrack then line up, or to land on 16, if ATC wants to do so. (I would argue that this is probably inappropriate for other reasons, but at least the takeoff scenario looks no more complex than would be a takeoff on 14.)
Second, notice that 10/28 and 16/34 intersect at about a third of the runway from one end. (A third down the runway on 10 and 34, two thirds down the runway on 16 and 28.) Even not considering winds, this would severely limit ATC's ability to safely use those two runways simultaneously, especially for heavier airplanes, as they would need to consider also the situation at the intersection in the case of a successful or a rejected takeoff or, in the case of a landing, an airplane either landing long or executing a missed approach. All of these add complexity and risk.
The ATC mantra is safe, orderly, expedient, in that order. Safety comes first, so anything that compromises safety in the name of expediency is going to be a no-go from the start.
If the airplane was "well behind" its scheduled departure time, yet just sits on the runway for a good ten minutes, my first guess would be that whatever caused the initial delay might be causing further delay before the pilots feel comfortable beginning their takeoff roll, or before ATC clears them to begin the takeoff roll.
As an aside, engines don't cause wake turbulence per se; wings providing significant lift do.

There are many reasons that departures from runway 16 might be delayed.
If an arrival to runway 14 has to go around, it would not have adequate separation from an aircraft taking off from runway 16. There would need to be a adequate spacing in the arrivals to allow for a departure from runway 16.
Departures from runway 16 will interfere with departures from runway 28. In addition, smaller aircraft departing from runway 28 would have a required delay after a large aircraft departing from runway 16, due to wake turbulence. They may prefer to get some departures off of runway 28 at closer spacing rather than make them all wait for wake turbulence.
As ymb1's answer shows, if both aircraft are departing to the north/east, their paths will also cross in the air. So if the controller decides to get the departures off of runway 28, they would need to wait for the last aircraft to get far enough east that there will be room for the departure from runway 16.
It's also possible that the aircraft have to wait for release so they can be integrated into the traffic flow. If they are significantly late, they may have lost their original spot in the flow, and it could take time before another opening can be made for them. This extends all the way to having a gate available at the arrival airport.
Any of these reasons could cause delays from departures from runway 16. Air traffic control would have them line up and wait so they are ready to go as soon as conditions allow. It sounds like heavy departures are the only use for the runway at the time, and if there's an emergency there are two other runways that ATC can use. ATC knows the traffic flow, and that they can afford to have an aircraft sitting on runway 16 waiting for takeoff.

In the event of an emergency that required the use of 16 for landing, ground control would get whoever was sitting there moved out of the way quite promptly anyway. Depending on the situation, even if the mayday aircraft were aiming for 14, they might move traffic off of 16 and the taxiways, just in case.

Don't agree with your first example. Runway 14 and 16 diverge, so in case of a missed approach on 14 at the same time as a departure from 16, the planes would be moving away from each other right from the start. Additionally, the missed approach procedure for 14 includes a left turn, so the go around would turn away from 16. Obviously during LVP there may still be an issue, but during normal operations I very much doubt this would have anything to do with it.


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What is black routing and red routing?
In a meeting with aviation experts, the terms black routing and red routing were discussed. What are they? From the discussions I was able to put together that either the TMU (Traffic Management Unit) or the controller can see two routes for a flight, a cleared route (black route?) and an agreed route (red route?).
I don't know what display they were referring to and if it was the controller that was looking at the display or if it was some traffic management display.

With no other information, I would think that one is the planned (ideal?) route and the other is the actual route, but I have no idea which one would be which.

It would be useful if you could add a geographical tag to this question, bear in mind this is a global website. The terms may very well be specific to a certain region.

Why didn't you ask in the meeting?!

Here's the history, at least for the US.
When I hired on, way back in 1985, the FAA had printers based on IBM Selectric mechanisms. They had a two-color ribbon, red and black, and a typeball with capital letters in two sizes, plus a few special symbols.
When a strip was printed, color could be selected by the computer for certain items. Callsigns on eastbound aircraft, for instance, were printed in red.
A red route appeared when an aircraft filed a non-preferred route to or from certain airports.
In the US, red is used for a PLANNED route or restriction - something the controller SHOULD do, but hasn't accomplished yet. As an example, if you filed KBFF..KDEN in your C650, the strip would reflect your filed route, but the computer would include a route over LANDR, like this - "KBFF.LANDR1.KDEN" (routing would be over AALLE, today)
That route would be printed in red, to alert the controller, and was the forwarded route. In other words, all subsequent positions would show that route in black, with no reference to the original filed route.
The controller issuing the clearance is expected to use the red coordinated route. If they choose not to (such as for a MEDEVAC), they must update the flight plan to force processing of the original route.
Today, there are no "red routes" per se, if you observe a preplanned route in EDST, it's highlighted in blue. Our strips no longer have two-color capability, so "red" text is now printed in black with a grayscale highlight.
The jargon, however, lives on!
To further address your example, if both a red route and black route exist in the system for a particular aircraft, that means the preferred route has NOT been issued, and some action must be taken. The controller with responsibility for meeting the restriction for that route will issue it, or force the computer to override the red route. Either way, it ensures that subsequent sectors get the right information.

The joke these days has to do with "old guys" calling blue routes in EDST "red", because we've all gone over edge.

In the terminal environment we would get what's called a Preferential Departure Route (I think) on the strip. The filed route KBFF KDEN would be bumped down a line, and above is the suggested route, enclosed in plus signs: +LANDR1 KDEN+. Only the portion of the route that needs to be modified is printed above. My facility's SOP is to highlight the plus signs in red pencil to draw attention to the PDR.

@randomhead, you'd be correct in the center environment, as well. That's the same way we display the route. I took a shortcut in my explanation. You can also put your own "red route" in, by doing a route amendment with the plusses. If I wanted to take the BFF departure over RAMMS, for instance, I could type "KBFF+..LAR.RAMMS1.+KDEN", and it will show my new route as the preferential arrival route. ERAM might still tell me to do otherwise, when the flight plan is activated.

Thanks for plugging this hole in history, and welcome to SO!  (Long live sed and awk, too.)

I really appreciate how you thoroughly explained this answer! Thank you kind stranger.


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Can anyone identify the plane in the image shown and/or year of service?
All I have is this photo, found in a collection of photo's which I'm trying to identify family members and an approximate date the aircraft is in service would help.  I've tried googling the aircraft Number but it only shows an Afro monoplane. The number is N 9732.
Any suggestions would be appreciated

It is a Royal Navy Fleet Air Arm Fairey III.D, with Fleet Air Arm serial N9732, not a Breguet 14, 16 or 17.
The markings are British - French aircraft have their serial on just the rudder within the stripes usually all in black (but occasionally all white), generally with a letter or letters denoting the original manufacturer or designer, usually above the serial number, and a specification table below it. A Breguet would have a Br or Bre either above the serial or to the left of it.
British aircraft from 1916 or so until the 1930s had the serial in an outlined format, on the rudder and/or the side of the rear fuselage in a much larger and more legible typeface. British serials for the RAF started with numbers, then after hitting 5 digits, they added a prefix letter and started over, then when those ran out, two prefix letters, all sequentially, so 9999 was followed by A1, A999 by B1, Z999 by AA1 however aircraft for the Royal Navy's Fleet Air Arm had a separate system of numbers, either as just a number, or as in this case, prefixed with the letter N for Navy - and to make it more confusing, the RAF also used an N, and had an airplane with this same serial number - an Avro Anson.
The serial number is listed at http://www.ukserials.com/serials-older-00naval.htm but because it is RN and not RAF, no other details are known.
The Fairey III.D first flew in August 1920, entered Fleet Air Arm Service in 1924, and was withdrawn from service shortly after 1927 when the streamlined III.F entered service. This machine was purchased in a batch whose serials ran from N9730 to N9791.
They were more commonly seen on floats, but could be flown as either a floatplane or a landplane.
Attached are a drawing of the III.D, and a photo of a similar machine.

Mike, welcome to Av.SE! Very nice answer, and extensive support & background info. Please continue to contribute here!

I think it may be a Bréguet 14. Compare it to this photograph:

You can see the same two sets of vertical struts on the wings, which are quite distinctive, and the wing looks like it has the same large flaps, plus the large forward tail section. The fuselage has the same two step holes (at least, I assume that's what they are) seen on this photograph, and the rear seat is also just visible.
The related Bréguet 16 was slightly larger, with three pairs of struts, so it's not one of those; there was also a related Bréguet 17 which seems to have been visually quite similar, but produced in much smaller numbers. I suspect it may be after the war, as it does not seem to have a gun in the rear seat, and the number on the tail doesn't seem to match the wartime style of numbering. They were still knocking around into the late 1920s/early 1930s.
Bréguet 14s were fairly widespread, but I think these look like French markings. However, I don't know enough to be able to speculate on what "N 9732" might indicate in that context.

Many thanks for the reply, the period 20/30s seems compatible with other photo's that show people in cars of 1930 vintage.  I'm less knowledgeable about aircraft so thanks again for the pointer.

I don't think the engine matches nor does the rounded front of the vertical stabilizer.


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What documents/procedures I have to follow to fly my aircraft from the UK to Norway?
I'm planning a trip to Norway for when Covid restrictions here in the UK are lifted, and was wondering what documentation is needed to enter Norway. I've already emailed AVINOR, and they simply gave me a link to toll.no, which yields no helpful information.
I'll be flying myself in a British aircraft. I'll be departing from Wick in Scotland and arriving in Kristiansand Kjevik in Norway. I'd like the details as if it were normal, pre-covid times.

This is fundamentally unknowable. Restrictions around the world have changed abruptly, sometimes with only hours notice. We don't know when the UK will lift restrictions to allow this sort of flight, and we don't know what changes the Norwegians will make in the mean time.

@CatchAsCatchCan I'm wanting to know the information as if it were normal pre-covid times.

My advice would be to contact the Kristiansand customs office and ask them that question. They are likely to be the most direct source for the answers you seek.

Are you flying in your own plane, or as a passenger on an airline?  https://www.udi.no/en/want-to-apply/visit-and-holiday/?resetguide=1 will give you some info, but not everything you need if you're flying in yourself.

Considering the "cessna-172" tag, I'd go with option A

I'm flying in myself.


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How does airfoil affect the coefficient of lift vs. AOA slope?
I'm trying to understand whether the airfoil shape can affect the slope of Cl vs. AOA (coefficient of lift vs. angle of attack) in the "linear" portion, e.g., from a few degrees negative to about 10 degrees. As an example, I picked 9 different airfoils from the NACA 4 and 6 series on airfoiltool.com and they all have pretty much the same slope in their linear regions (Rn 1'000'000):

The question I have is, if I would like a steeper slope (more effect on lift with less change in AOA) are there specific airfoils I should look at? Or any specific airfoil characteristics? Or is this slope basically given by physics for "reasonable overall well-performing" airfoils?

This very good YouTube lecture by Andrew Ning at BYU has a thorough explanation of thin airfoil theory and why the lift slope dCL/dalfa of any airfoil is roughly 2*pi per radian (or about 0.1CL/deg) of angle of attack. This result is derived and finally appears about 49-50 minutes in Andrew's lecture. https://www.youtube.com/watch?v=VD0SP0RAPd0.

The airfoil affects the lift curve slope only very little; theoretically the slope should be a bit steeper for thicker airfoils.
But that pales in comparison to the effects of wing planform. Here the biggest influence is from the wing's aspect ratio and sweep. Another factor is the flight Mach number and the Reynolds number.
But there is one trick to artificially increase the lift curve slope for a given planform and flight speed: Add a camber flap and move it in sync with angle of attack. This will shift the zero-lift angle inversely to the change in angle of attack. A purely mechanical solution would use a flap with a large control horn, so that $c_{r\alpha}$ becomes positive while $c_{r\eta}$ stays negative. However, this is prone to flutter at higher speeds, so depending on the planned speed range a hydraulic or electric actuator, driven by a control unit which is hooked up to an AoA sensor, might be the better solution.

Do you have a link or short explanation for why the lift curve slope is not (cannot be?) affected by airfoil shape? Thanks for the flap links!

@TvE Potential flow theory. And lots of windtunnel data. Follow the links in the answer or ask more specifically. As it stands, this question is on a level of "why can I not change gravity". You can't.


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What Paper Format do Boarding Passes use?
I'm looking at creating some Boarding Passes for my Virtual Airline called "Zelandas". After looking at websites like the SITA website, Wikipedia, and more, I cannot seem to find what format of paper is used for a Boarding Pass.
When I am talking about Format, I mean something like A4, or B5 etc.
Where would I be able to purchase this kind of paper, not in bulk?
Thanks, Will

Send the boarding pass to a smart phone. Ryanair allows printing of your own boarding pass. It's a PDF and the A4 page folds to A6 (quarter) size for pocket storage.

I'm not sure boarding pass' format is normalized. Moreover, this question may be better suited on travel.SE

I'm voting to close this question as off-topic because it is a better fit on Travel.SE

Standard boarding passes are the size of an IBM punchcard, 7⅜ by 3¼ inches (187.325 mm × 82.55 mm) because paper and printers in that size were readily available at the time, and then inertia kept the size the same even when punchcards fell out of use and it became a specialty item.
Many airlines have switched to rolls of 3⅛ inch (79.375 mm) thermal paper, as is now commonly used in cash registers. For a new system, this is probably less expensive and easier to prototype.


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What are the exact dimensions of a B-2 Spirit?
I want to make a 3D model of a B-2 Spirit bomber. However I'd like to know the excact dimensions of it so that I can make it at least somewhat accurate.
I'd like to know the lenghts of the following red lines(each straight line separately):

I doubt you will find an official source for these. I'd look for a B-2 on google maps/Earth and use the distance measuring tool.

I am working on getting some info from the official, unclassified documentation. But I'd appreciate some help from others.

Have you asked DOD about that?

Did you even consider what I suggested? I found a B-2 on google maps in less than 5 seconds google search

Could you please send a link? I can't find it.

@MichalŠtein https://www.google.com/maps/@38.7250446,-93.5602627,145m/data=!3m1!1e3?hl=en

I doubt you will find an official source for these. Luckily, we have google maps.
Using this example from Whiteman AFB (https://www.google.com/maps/@38.7250446,-93.5602627,145m/data=!3m1!1e3?hl=en) and distance measuring tool we get the following lengths:

1 - ~4.65 m (~15.24 ft)
2 - ~3.69 m (~12.10 ft)
3 - ~7.83 m (~25.69 ft)
4 - ~10.71 m (~35.13 ft)
5 - ~4.58 m (~15.04 ft)
6 - ~31.52 m (~103.40 ft)
The rest you can get from the published dimensions (height, length, wingspan), as an example.

Nice.  You seem like the type who might be thinking about joining the upcoming Area 51 invasion?

I live in Europe but I can give support.

Just like in the story about the B-2s unveiling, where some journalists (allegedly) overflew the site to get pictures of the planform and tail, which the military was not keen to show.

What's the other aircraft next to the bomber? A T-38 Talon? There are two more on the other side of the hangers as well.

@DarthPaghius Correct


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What happens to Vyse and Vxse above the OEI ceiling?
An EASA ATPL question/answer insists, counterintuitively, that a twin which loses an engine and must drift down will find its least rate of sink at Vxse. I've been trying to understand this, but haven't come up with an answer yet. Do Vy and Vx even exist as concepts when above the ceiling? Does "best rate of climb" become instead "least rate of descent"? Does "greatest distance between the power-required and power-available curves" become "least distance" between same? Would the speeds of Vx and Vy (with or without SE) change when going from below ceiling to above while at the same altitude and mass?
One way to determine Vx and Vy is to look at a ROC vs Speed chart, where ROC will be an inverted parabola. The peak of the parabola is Vy, the tangent of it to the origin is Vx. If the whole curve is shifted below the x-axis, however, the tangent will fall on the far side of the Vy peak. So I would expect Vx > Vy when above the ceiling. But that still doesn't help understand why EASA would say least sink is at Vxse.

Vx increases with altitude while Vy decreases with altitude.  When they coincide, you have reach the airplane’s absolute ceiling, which it can no longer climb and can only maintain altitude at that specific calibrated airspeed.  Vx and Vy do exist above you maximum single engine ceiling, however, should an engine fail above the maximum single engine ceiling the airplane will begin to descend in order to maintain a given airspeed.  Pitching the airplane for blue line, Vyse, and maintaining the correct bank angle in the direction of the good engine (3°-5° typ.) will result in the minimum descent rate during drift down.
I have no idea why EASA would state that the airplane should be flown at Vxse above the maximum single engine altitude to minimize drift down; every source of information I’ve ever encountered indicates your airspeed should be maintained at Vyse, in addition to maintaining proper coordinated flight with OEI, in order to minimize your drift down rate.  This makes sense, since the airplane will have the most power available to it for climbing and will result in the least loss of altitude over time in this configuration vis a vis conservation of energy.

this may be a play on minimum power for level flight vs Vy, but I definitely agree with you for 2 reasons:  1. Asymmetric flight is easier controlled at Vy.  2.  Vy will get one to their safe landing field faster and more efficiently.  The question may be a bit myopic.

But is minimizing the drift-down rate the goal? Shouldn't it be minimizing the drift-down angle?

Why would you want to minimize the drift down angle?

@CarloFelicione, because I want to land as soon as practical, and want to stay as high as possible on the profile in case there will be some additional problems. And shallower angle means being higher on the profile, while the flight is faster, so the landing is sooner.

If you want to remain as high as possible to conserve altitude, you’re going to want to descent at Vyse.  That will result of the lowest possible loss of altitude per unit time, and keep you in the air as long as possible.


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How is half of the wing strut (high wing) [or half the aileron (low wing)] a good reference to estimate gliding distance?
Through training and still to this day, I keep on using these reference points to judge if I am at the right distance from the runway or the field I aim to land at (forced landing).

Use of such references is dependent on the aircraft.

P.S.  Your confusion is unclear and that is why you are getting the close votes.  If you knew the exact glide angle of your aircraft, and depending on seat position you could correlate it to a feature on the airframe that would give you the ability to estimate whether a geographic feature such as a runway or field is above or below your glidepath, that would be useful.  That is "how" it works, but a general statement for all high and low wing aircraft is neither accurate nor useful unless you put in some qualifying statements.

Those little short cuts are just to get you started. You need to learn to judge those things just by the sight picture so aren't dependent on aircraft specific crutches like that.

I suspect this is just a rule of thumb thing that works out just about right.
The geometry will have to do with the approximate height of your head vs the strut/aeileron, the altitude of your aircraft (when you commence a PFL) and the glide ratio of a typical trainer  working out just about right to glide the distance to that point.
You simply do not have time to do complex calculations of glide range from the 1000-2000ft you would normally commence such an exercise. So a basic rule of thumb, that you can use by just turning your head, is as good an estimation as any. If it works, it works.


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How would I draw the Max Thickness Sweep Angle on a wing from a Top View?
I have the Max Thickness Sweep Angle, Wing Tip and Root Chord Length, and Max Thickness to Chord Ratio defined. However, I am having trouble drawing the Max Thickness Sweep Angle on the wing because I'm not sure where to start on the root relative to the Leading Edge of the wing. In essence, I am trying to find where the Max Thickness Sweep Angle is on the root and tip of the wing from a Top View of the wing. Any tips are appreciated!

Start where the wing is thickest?

Do you have root and tip airfoils? If not, you will fail.


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Does an increase in Mach number lead to a decrease in Total Pressure Recovery (TPR) for supersonic inlets?
I am curious if the total pressure recover for supersonic inlets, in general, decrease for an increase in Mach number.


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What does it mean to have a SIC limitation on your medical class 1
Is there anyone who knows what a SIC limitation on your medical would mean? I found out on the EASA documents that it stands for "Specific medical examination pilot". But what exactly would a SIC change for someone (if anything).


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What does it mean for a wing's lift distribution to be elliptical when the planform is not?
How would you go about finding an equation for the lift coefficient of this wing where the lift distribution is known to be elliptical but the planform is not?

The (local) lift depends on many factors - not only the chord but also the profile, angle of incidence - and even up to the actual local flow. Without knowing the details of the actual wing, the distribution of lift can be hard to calculate.


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How to calculate the zero lift drag coefficient for a wing with data from airfoiltools.com?
I'm currently trying to write a script in python that I can use to optimalise a flying wing aircraft. I've run into a problem when trying to use data from airfoiltools.com. I've tried to calculate the zero lift drag coefficient using a value for Cd and Cl found on airfoiltools.com, I used the following equation:
Cd = Cd0 + Cdi
Cd0 = Cd - Cdi -> I then substituted the induced drag coefficent:
Cd0 = Cd - Cl**2/(piARe)
The symbols are:
Cd0 = zero lift drag coefficient
Cd = total drag coefficient (from airfoiltools.com)
Cl = Coefficient of lift (from airfoiltools.com)
AR = The aspect ratio of the wing
e = The oswald efficiency factor
The problem is that this equation gives me a negative value for Cd0, which is not possible for obvious reasons.
Please, does anyone see my mistake here? I'm not formally schooled in aerospace engineering so I don't know all the theory behind these equations, thus I may not understand wether I can or cannot use them in this situation.
Thank you in advance and kind regards,
Remco van Woerkom

Induced drag is only produced when real lift is created. In 2D flow, when only the airfoil drag is given, there is no induced drag even for discrete lift coefficients. 2D flow assumes an infinite aspect ratio which results in zero induced drag.
Your zero lift drag coefficient should be the airfoil drag coefficient at the actual lift coefficient at the wing station when the airplane is in flight. Do this for several stations over span since the lift coefficient varies over span. Plus the contributions of fuselage, tail and whatever is added to the configuration, of course.

Ahh that makes a lot of sense! Thank you that helps out a ton. However could you elaborate on how the lift coefficent changes over the span of the wing? Or maybe reccomend a paper or article to read that explains this in more detail? I would love to understand it.
Thanks!!

@RemcovanWoerkom I recomment this and this answer.


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Find the course or heading of an object
Im working with orientation using GPS + IMU, and before the actual implementation of the program, im working with simulation using a dataset that provides me some GPS data, such as latitude, longitude, elevation and bearing, with this information, is there any way to find the heading or the course information of the object? Like the one given by the nmea VTG packet.

"is there any way to find the heading or the course information of the object?" is not very clear. By 'orientation', do you mean 'TO' an object? Do you need to know the course 'between' 2 objects? Do you need to know the distances too? Many IMU's today have a magnetometer sensor on board to give you instantaneous heading of the unit. You need a simple course/distance calculation module for your dataset.

I need the orientation of an object with respect of magnetic north, i have found that with magnetometer data i can find this information.

Does that cover everything you had on your mind for your post?

Yes, im working with GPS + IMU fusion and the orientation and coordinate frame is my biggest problem now. The system dinamics and covariances matrix i already solved. I'm new in this topic so, i'm discovering how this things works, i have found Madgwick filters to solve this problem.

No.
Knowing Lat/Lon, elevation, and bearing (and, presumably, distance) from a known reference point, the current track or heading could be anything.
It's like saying, if you know where I am, can you tell which way I'm facing (or walking)? Given one data point, you can't. Over time you might plot the points to work out the track, but that's your result, not given by the data per-se.

Thank you for your answer, i will search for other dataset that give me the heading.

And of course be aware of the difference between heading and track, although it sounds like you are already.


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Private Pilot Compensation
I am a new private pilot. My parents want me to take them flying. I do work and have a bit of my own money, but compared to the cost of flying it is not much. My parents paid for most of my training. I am still in high school, so I live with them and they pay for most of my existence. Obviously I cannot be compensated for flying them, but I wonder if there is any legal way for this to happen. The same question can be extended to when I take friends flying. Would it be as simple as me using a card that draws from one of their accounts? Me paying but with their money. Any knowledge/advice is appreciated, I would rather not break FAA regulation on my first flight as a private pilot.

Related: If “flight time is compensation”, how can a PPL holder legally fly at all?

Does this answer your question? If "flight time is compensation", how can a PPL holder legally fly at all?

Not a dupe. The "parents" aspect of this question isn't addressed the the suggested dupe at all.

For your parents, just pay for the rental yourself and take them up. They're your parents, they want to see you do something "special". Don't bother them about money, especially if you're living at home. (Basic rule of thumb - if your parents are paying for your cell phone, you're not "independent").  For your friends, I suggest telling them, "Sure, I'll take you up if you pay the rental fees". Then tell them how much rental, etc costs. Hopefully that'll be the last time they mention it. :-)

@BobJarvis-ReinstateMonica "Sure, I'll take you up if you pay the rental fees" Isn't that illegal? Pilot has to pay at least pro-rata share (in the U.S., at least,) no?

"It's illegal for X to happen, but I wonder if there's any legal way for X to happen"

@user253751 Well, the issue of parents paying for a minor does create a different situation from the normal one, since there's legally (and practically) little-to-no difference between a dependent minor paying for something and their parents paying for it. So, that part is certainly a fair question, at least.

The short answer is that in practice the FAA doesn’t care about “compensation” between family and bona fide friends.
The long answer is that the FAA’s mission is to protect the general public from pilots. (If they also happen to protect pilots, that is a side effect at most.) Your parents and bona fide friends are not the “general public”.
As a practical matter, the FAA could never prove beyond a reasonable doubt in court that any particular dollar that your parents or bona fide friends gave you was for flying vs a gift or for something unrelated, especially when it is likely they would be uncooperative with any investigation or charges against you. If they give you money, and you happen to use some of it to take them flying to a place of your choice, so be it. It’s just not worth the FAA’s time to look too closely at that, so they consciously turn a blind eye.
Where you will get into trouble is flying strangers or acquaintances to a place of their choice. The exact path the money takes is irrelevant; if you accept compensation from the “general public”, then you are operating an illegal charter, and the FAA will hit you like a ton of bricks for that.

This is the best, most common sense answer to this sort of question that I have ever read.

The question is if the money given to you by your parents can be considered income. In the case of a parent paying for a legal dependent’s expenses, I do not think this can be considered income. Regardless of how the expenses are paid. This would not be considered flying for compensation. Friends paying for your flight time would fall under Part 61.113. A non-family member does not have a previous benefactor-dependant relationship.
An indication of this is how the IRS treats money exchanged between parents and dependent children as opposed to money exchanged between people who are related in a different manner. Even when money is exchanged between parents and non-dependent adult children, it is considered a gift instead of dependent support.
To make it clear, your parents can pay for the expense of your flight time. Your parents can pay for the expense of flying them as long as it is not required of you to fly them as terms of payment. Your parents can pay for the expense of flying a friend or friends as long as they are not requiring it of you as terms for payment.
No one else can pay for your expenses to fly property, another person, nor themselves. You can not receive any income or compensation from any source for flying. Someone besides your parents paying for your pro rata share of expenses would be considered compensation when flying other people or property.
However, there is not a prohibition on someone paying for your expenses to fly yourself solo. Just as long as it is not in the furtherance of a business or part of your employment. And, there is no prohibition on someone going you a monetary gift that you can spend freely on anything you so choose.

I meant parents paying for me to take friends flying, which it seems like it would fall under the same category of non income. Thank you!

@Dean F But those provisions are for passengers sharing expenses no?  if he's getting fully reimbursed to take non family members flying, it's getting a little grey I think.

@mvpg: Your parents give you money - an allowance, or a Christmas or birthday present.  How you spend that money is up to you.  Unless they put something in writing that says a given amount is specifcally for taking your friend(s) for a plane ride, I can't see  how it would be a problem.

@mvpg - If it is the parents of the dependent pilot paying, there would be no conflict. It is not income even if the pilot takes non-paying passengers along. There just can not be a stipulation that the non-paying passenger has to accompany the pilot for the parents to pay. It must be strictly optional or coincidental.   If it is the parents of the passenger who are paying. And, there is no dependent relationship with the pilot, then it is income and falls under the provisions of Part 61.113.

@JohnK - Part 61.113 says that a private pilot can not be compensated in full or in part for flying of passengers nor property. Cost sharing is allowed as long as the pilot pays their pro rata share. So, it would not be a grey area. If the money were given by the parents of a dependent pilot, the money would be treated as the equivalent of the pilots own money. As long as the funds did not carry the stipulation of carrying the non-family member. If the pilot is charging for the act of carrying passengers, that is black and white regardless of who is getting charged.

Another great answer.  So often these discussions degrade into questions over who's idea it was to go flying in the first place, and what you plan to do when you get there...

I believe you are able to split the maintenance fees with them. Then, as you know, once you obtain a commercial pilots certificate, you can make money. However, until then, you can‘t even have your passengers pay the full maintenance fee/flying fee. Also congrats on your Private Pilot Certificate. Have fun flying!

Corrections have been made to your answer. Feel free to roll back the edits if you disagree with them. Also, a private pilot can charge the passengers all the expenses of the operation of the flight itself to include fuel, landing fees, oil, other fluids, and other costs directly related, minus the pilot’s pro rata share. Hangaring and tie-down fees at the domicile airport, and routine/scheduled maintenance and repair fees can not be charged. If all of the above and other operating costs are wrapped into a flat rental fee, the rental fee can be shared. But, not any association fees or dues.

authors: Bob Jarvis - Слава Україні


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How to interpret flight schedule data from before 1987
I'm trying to interpret schedule data from before 1987 (see example).
Example line:

20100001409B000 033504140079100000000000000000D004BOSJFK  RC0970AS     1234567  0535 BOS 0654   JFK RC 970 YQ   CVR 1           \

I'm trying to understand if this flight represents a direct flight.  Specifically, my understanding is that the 9B (byte 11-12) indicates that it is a "certified direct flight". However, the 1 (byte 117) after the CVR (bytes 113-115) seems to indicate the number of stops, here more than zero. I'm trying to figure out what it means if a direct flight has stops. Some of these "certified direct flights" in my data have more than 4 stops on a short route that would not have needed a refueling stop.
Does anyone have experience in interpreting these older schedule files?

There is a distinction between a direct flight and a non-stop flight. Is that the source of the confusion?

In short, direct flight means one flight number, nothing else. In particular, and somewhat counter-intuitively, it doesn't mean no stop or even no change of aircraft.

From which tool/system does that come from?

Looks like the OAG SSIM file. Have you asked OAG directly?
I have the detailed record spec but not immediately available.

not sure, but seeing the "BOSJFK" and then CVR hints at this being a flight Boston-JFK-Vancouver. And there's your single stop. And most likely it's the leg from JFK to Vancouver.


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What does the red background of some toggle switches in CRJ 700/900 overhead panel mean?
I've noticed, that some of the toggle switches (e.g. DC Switch or the four Hydraulic Pumps) have a red Background whereas others (e.g. GEN1 and GEN2) are unpainted.
Here you can see what i mean.
Is there a special meaning to the red color? First i thought that systems marked with red require a running ENG or APU. But the red on the DOME Light switch obviously does not match.

Does the color change between airframes, or are red switches always used for the same switches?

@mins See ymb1's (now deleted) answer. It seems consistent at least since the 200 variant.

@Bianfable: Precisely I have a doubt on the fact they are the same, e.g. on this comparison from two links provided in the answer this is not obvious the same switches are used for A/C fan or windshield anti-ice. In addition on the LH picture A/C fan is bistate and red while on the RH it seems to be tristate and uncolored, which is the contrary of the Hydraulic panel scheme.

There isn't actually any particular meaning to those colours. Those switches have a rubber boot at the base to seal out moisture and outside dust, etc, and the rubber happens to be red because that's what the supplier used. Lever Lock switches like the Gen switches don't have a visible boot (the seal is internal) and a couple of the other ones have no boots or boots that are grey rubber because that happens to be what that particular switch came with.

I'd really like to upvote this, but my gut says there is always a meaning behind the choices of colors used in control panels.

I was on the program for 25+ years and I can tell you the colour of the rubber used in the dust boot has no relationship to anything.

Well, there you go.

@JohnK   Even then, the colour still means something - the supplier/manufacturer of the switches isn't going to change their colour in the middle of a batch...

They'll just follow the spec for the switch, which might say something like "Boot material of silicone rubber, colour red, to MIL-S-XXXXXXX".  As to why red, or black, or grey, if there are any, the reasons are lost to the mists of time...

I've seen switches like these for years in many applications, they're not just in airplanes.  Red for whatever reason seems to be the most common color for the rubber.  Maybe because it's easier to see if the seal is damaged and needs replacing than with a black seal?  Being rubber, they do tend to dry up and crack over time.

@DarrelHoffman Glass jar rubber seals are red. Rubber bands are (used to be at least) red. The seals on my blender are red. Red just seems to be the most common color for rubber in general.

I think there's a reason. That red/orange color is very commonly used to denote the material is capable of handling high temperatures, and I suspect it's used because the polymer is flame retardant. I think it's originally because it imparts the look of brick and clay, as well as being a bright color so that cracks are easily visible. Examples include bleed air ducts, firestop in buildings, welding screens, insulating gloves and mats for power lines, and silicone oven mats.

Yeah things like fire sleeve and Scat hose are that colour, but it's just a dye so you can make it any colour you want.  Some firesleeve is black.  Temperature resistance isn't an issue with these switches.


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Could the static charge build up during flight be sufficient to power aircraft systems?
Aircraft build up a static charge during flight which is currently discharged through static dischargers:

I recently read the abstract and summary of this paper:https://www.sciencedirect.com/science/article/abs/pii/S1359836820334235
Which explores using certain types of polymers with conductive cores (graphene) for aircraft bodywork and wings to utilize the static charge build up over the aircraft surface to act as a large capacitor. For example, this would be achieved by creating a potential difference across the wings.
What magnitude of energy could be created and what systems could this run - if any? Would this be relevant for commercial airliners, electric aircraft, civilian aircraft or even superlight solar powered aircraft, such as the Solar Impulse which flew round the world.

I understand there would be a weight increase with additional equipment but I am wondering about the feasibility and whether it would even power a clock on the dashboard.

Here's a very back of the envelope calculation for precipitation static:

The wetted area of a 787 is around $1800~\rm m^2$
The most triboelectric materials are around $.2~\rm nC/g$
The density of water in a cloud is at most a few $\rm g/m^3$
The cruise speed is on the order of $300~\rm m/s$

Putting this all together gives a few hundred microamps of current at maximum. Even if you develop a few thousand volts of potential difference across the plane, this amounts to around a watt. Enough to power a clock maybe but certainly not enough to power an instrument panel. By comparison, a ram air turbine produces thousands or tens of thousands of watts.
This estimate is likely much too high- the density of clouds decreases with altitude, and 787s do not spend much time at cruise speed at low altitude.
One watt is certainly not anywhere near enough to accept any weight penalty to the airplane.

One watt, that you only get sometimes... definitely not worth adding weight to an airframe that's optimized to be as light as possible!

Just for the record, a wristwatch uses vastly less than 1 Watt of power.  How much power does a wrist watch use to function? estimates 12 microwatts for a wind-up mechanical watch; https://www.quora.com/How-much-energy-does-a-typical-digital-watch-use-per-year estimates 0.7 microwatts for a battery-powered watch with an LCD screen.  (0.006 Watt-hours per year estimated from battery capacity).  A clock with an LED display or a backlit LCD might use a few milliwatts: emitting light costs vastly more than keeping time but still not much.

@PeterCordes From a cursory check, many instrument clocks use several watts. Presumably there is no strong impetus to optimize the power draw since it is negligible compared to everything else.

@Chris: That makes sense; I'd guess a typical plug-in clock-radio might use a whole watt (even with the radio part off). I only noticed after commenting that the question specifically asked about a clock on an the dashboard.  If you had to power a clock from triboelectricity, just as an exercise in silliness, you could, though.

@PeterCordes those LED clock-radios draw about 5W. They get slightly warm, which is a good indication, but I measured one once (I reduced my background power consumption at home by nearly 200W of little things)  It would probably be less weight to power the clock off a few lemons!


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Do the spaces between runways and taxiways need to be grass/scrubs?
I travel often for work and have often wondered why you don’t see more variation in the vegetation in between the runways and taxiways.  It is almost always short grass (Or in desert areas scrub). It is often easy to quickly find airports on satellite images of urban locations because they have the most open grass areas for miles around.  Take these two examples (EWR and LAX):

Is there any regulations, restrictions or custom which would prevent the airport from planting wild flowers or even low crops in those open spaces? I can obviously see why planting corn or something tall would be hazardous, but it seems like a waste of open space. Additionally, it takes a lot of water to keep all that grass alive.
I also realize that crops would create some logical issues with the farming equipment crossing the taxiways, but they need to mow the area now so that would probably not be insurmountable.

You don't want to plant anything that would encourage birds.

Not all green is grass: What are the areas marked in green around the taxiways?

Re "it takes a lot of water to keep all that grass alive", not if you use native grasses that are adapted to survive on natural rainfall.  Which is why you're likely to see sagebrush &c in desert areas.

At many less-urban airports crops are planted on airport property, to include the areas that would be inside a hypothetical box enclosing all the runways. But they are not (to my knowledge) planted between runways and taxiways.

For a moment I thought that was one photo & the climbout from rwy 19 at the northern airport would be 'interesting'

@ymb1  That is exactly what I was looking for. Paragraph 2.10 in the linked circular spells it out quite clearly.  It seems like it is discouraged but not forbidden as long as it doesn’t increase wildlife activity.

I’d think you also don’t want plants that could end up producing a bunch of dried-up waste that could become FOD.

Here are just two examples of crops planted at airports: at IOW along the edge of the runway safety area and FAR between the taxiways! On Google Maps it may be difficult to see but other imagery (e.g. what is shown in Apple Maps) clearly depicts corn.

Regulations are obviously going to vary by country, so you'll need to specify which country you're talking about to get an answer on legal matters. I will say that I don't know of any country off the top of my head that regulates the vegetation on an airport, but I'm not exactly an expert on foreign law, so take that as you will.
The main reason to keep the vegetation short is to eliminate bird habitat in order to reduce the risk of bird strikes. Bird strikes cause the industry billions of dollars per year (not to mention the people killed in bird-strike-related incidents), so airports do whatever they can to try to keep birds away, and one big technique is to eliminate any plants that may attract them.

Just to add: tall grass (or shrubs) may encourage nesting. Too many wild flowers will pull insect, and so birds which eat insect. Crops or any plant seed will pull other birds. And rabbits and foxes are also problems.

Also tortoises in wet areas. Fortunately tortoises mostly don't fly, or veerrryyy slowly.


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Calculating CL and CD from Cp vs. x/c graph data?
I need to calculate CL, CD, CM coefficients for NACA 0012 airfoil at angle of attack 6 degrees and Re=7.5e5, Mach=0.05. I used Xfoil for getting the CP distribution, Cp vs. x/c graph and Cp-x-y data. With Cp-x and Cp-y data points I tried to calculate CL and CD values with a matlab code with equations given below;

I integrate the CP-x, CP-y points which executed with XFoil respectively to getting Cx and Cy. I used trapz command in matlab to integrate these points. However at the end of my calculation matlab code was found that CL=1.1936e-04 and CD=0.7249. However at the graph screen of XFoil CL and CD was different.

I can not understand that if the problem was about my solution method or my matlab code? How can I get the  coefficients with Cp distribution?

You have done it correctly. Only mistake appears to be swapping the CL and CD value.
Being said that, for the info, this CD mearly is a numerical error due to ds being finite as invisvid flow drag is zero.


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How can an all flying rudder be almost 100% more efficient than a vertical stabilator and rudder?
How can an all flying rudder be almost 100% more efficient than a vertical tail and rudder?
According to the Zenith school of aircraft design, a rule of thumb for the size of an all flying rudder is 7% of wing area. For a classic vertical tail and rudder, the rule is 12%.  That's an increase in area of almost 100%!!
A classic rudder foil, something like a NACA0012, has a max cL of roughly 1.5.
A vertical stabilator and rudder is like a wing and an unslotted flap, which adds cL of about 0.7. That's a total cL of about 2.2, which works out to an increase in efficiency of 50%.
So... why is an all flying rudder 100% more efficient, if a vertical stab and rudder produce 50% more lift?

Exactly what is happening?  What are the conditions?  Presumably your comparison does not involve a test of weathervane stability, with the pilot's feet off the rudder pedals!

Yes, this would include weathervane stability with the pilot's feet on the rudder pedals.

Because on the Zenith the massively slab sided fuselage is the vertical stabilizer, and the rudder is still the rudder.  The surface area of the all flying rudder is about the same as the rudder on a normal plane, and it depends on the fuselage for weathervaning tendency.   There's no free lunch.  If you build a Zenith with a skinny boom tail and the all flying rudder, it will be quite marginally stable in yaw, like a Fokker DR-1.

The slab sided fuselage would definitely be used in the tail volume calculation

I would caution against comparing the effectiveness of stabilizing surfaces using CLmax, or generally any surface using CLmax alone (see related question: What happens when you put vortex generators on both sides of a symmetrical vertical tail?). The efficiency of an aircraft is more than its maximum lift.
Sure, a rudder is a plain flap. But why do you need rudder, other than coordinated turn? I can think of two operational scenarios: crosswind landing (1), and trim for asymmetry (2).
In (1), the maneuver is initiated at zero sideslip, hardly CLmax which corresponds to high flow incidence. Once you are established in a steady-state wings-level skid (fully de-crabbed), the sideslip is actually opposite of the rudder deflection. The CLmax for plain flap is inapplicable.
In (2), the worst case is one engine inoperative. Sideslip here could be positive or negative, depending on whether banked into the live engine(s). Still, the sideslip is not near the maximum incidence.
Now onto the all moving rudder vs. traditional stab+rudder, all moving rudder has a larger surface area so it's a more effective rudder. However, I would caution against decreasing the overall tail volume since it affects your weathercock stability and dutch-roll. That's not accounting for other factors such as heavier actuators for all moving surfaces.

You also need tail volume for yaw control, especially in slow flight, getting out of a spiral

When we deflect the rudder to create an intentional sideslip, the net sideforce from the fin-rudder combination actually acts in the WRONG direction-- OPPOSITE to the direction that we are trying to shift the rear of the aircraft.  The fin is "fighing" the rudder.  Therefore we have more rudder power-- we can achieve a higher sideslip angle-- if we get rid of the fin.
This is explained in more detail in this highly related answer -- How is a sideslip maintained (aerodynamically)?
On the other hand if we are just trying to use the rudder to oppose some other yaw torque (such as P-factor) and maintain a zero slip angle as measured by a yaw string, then the fin isn't "fighting" the rudder any more and the rudder might be more efficient when the fin is present than when the fin is not.  However, if we are talking about a fixed total area of fin and rudder combined, it's not hard to see even in the zero-slip condition, the all-moving rudder would have more power than a smaller rudder plus a fixed fin.

For passive yaw stability, the rudder does nothing.  It just wants to trail unless you hold it centered with your feet.  You can add the rudder into the passive yaw stability equation by adding an anti-servo tab or installing bungee centering springs which tend to fix the rudder at neutral so it contributes to passive weathevaning to the extent of the spring stiffness.  Cessna 180s and 185s use centering spring bungees to provide enough yaw stability to require no additional fin area when on floats.  The force you have to apply to overcome the springs is a pain though.

@JohnK -- true-- as noted in my comment under question, we have to ask exactly what is being tested.

Future edit: add link to Zenair webpage-- "Rudder" section mentions virtues of all- moving vertical fin for exceptional crosswind performance ( i.e. ability to attain large sideslip angles).  http://www.zenithair.com/stolch801/design/design.html

I've flown the Zenith 750 with the demo pilot in Mexico Missouri and yes it had a lot of yaw power and I don't recall it being squirrely in yaw, so I guess the fuselage side area does the job.

I still don't see how the fin is fighting the rudder. Deflection is lift. A classic NACA foil generates max lift at about 15deg at a cL of about 1.5. Add a stab with a gap and the vertical tail becomes a "slotted wing with a flap", which adds a cL of about 1.3 for a max cL of about 2.7. That's generating almost twice the lift, not less lift , providing you're deflecting the rudder at about 15 deg.

@Fred - I'm not sure how to explain it better.  If the rudder is used to create and maintain a large sideslip angle, isn't it clear that the fixed portion of the vertical fin is creating a yaw torque that would tend  to reduce the sideslip?

Hmm: I'll have to think about this a little more. If you're in a coordinated left turn, say the rudder is deflected to the left at 15 deg, it's generating say 100 lbs of lift to the right, with a cL of 1.5, swinging the tail to the right, turning the plane left. Add a stab and a 50% slotted rudder and the rudder/stab will produce double the force to the right, or 200 lbs, as the stab and slotted rudder produce a lift to right at a cL of almost 3.

@Fred - we seem to be talking apples and oranges here.  Many of my comments are about a situation where a great deal of (intentional)  sideslip is present, not about coordinated (non-sljpping) flight.


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How to determine individual wing loading of a triplane for stress analysis?
How to determine individual wing loading of a triplane for stress analysis?
I understand that a monoplane must be able to withstand the weight of a plane x a load factor, say n=4, for a standard flight envelope, and also asymetrical loading.
What about triplanes?
Should each wing carry 1/3 the load?
Assuming 1 deg decalage each for the 2nd and 3rd top wings, they will stall before the bottom wing.
But.... you could have a situation where the top wing is stalled and the bottom 2 wings see the full load of the plane
And... you could have a situation where the top 2 wings are stalled, and the bottom wing is subjected to the entire weight of the plane.
So.... how strong do you have to make each wing of a triplane?
Of course, if the plane has struts, all 3 wings would be part of the equation.
My gut feeling is that the top wing should be 33% loading, middle wing 50% loading, and bottom wing 100% loading, and then model the wings as 3 joined cantilevered beams.
Is this correct?

A stalled wing will still produce considerable lift, so it is not on - off. That said, the best you can do is to model the lift distribution at least in a vortex lattice code which correctly computes the mutual interference. This will give you very good results for attached flow and unstalled wings.
But triplanes have successfully been designed before the availability of computers, so for a first approximation distribute the load according to the wing incidence. Lift will be proportional to the angle of attack of each wing, calculated from the airfoil's zero-lift angle. Stagger will increase the local angle of attack of the forward wing and vice versa. How much depends on the ratio between stagger and vertical wing distance. The first solid theory of lift distribution was developed by Ludwig Prandtl and his pupil Max Munk, whose tabulations can be found in NACA Report 458 which is for biplanes but can be extended for triplanes.
If you like more recent literature: Even a publication from 2009 refers to Munk's tables, so they should still be relevant today. However, it finds a lift difference between positive and negative stagger that – according to Munk – should not exist.
Note that with struts and inter-wing bracing the whole triplane is your bending beam and will collectively carry the lift loads. Only with cantilevered wings will you need to worry about the root bending moment on individual wings. Bending between struts needs still to be carried by the single wing but will be small compared to the root bending of a cantilevered wing.


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What area is used to determine the horizontal and vertical tail volumes of a vtail?
What area is used to determine the tail volume of a 45 deg vtail?
Is the same entire area of the vtail used to calculate vertical and horizontal tail volume?
or do you use the projected areas in the x and y directions for horizontal and vertical tail volumes, respectively?
or other?

Depends on what the tail volume is used for.
For control authority and trim: Use the projected area.
For flight dynamics and damping: Reduce that by the cosine (horizontal) rsp. sine (vertical) of the V-angle, in your case multiply the projected areas by 0.707.
The control effectiveness of a control surface is proportional to the cosine of the V-angle, but the damping characteristics go down with the square of the cosine.

I wouldn't worry too much about controllability. Initial sizing is all about stability (ie damping). So tail volume should be computed with cosine and sine squared. In any case, mixed control tend to overwhelm one side anyway, so it's not like you'll have too much controllability.

So... which area should be used when using standard horizontal and vertical tail sizing ratios?   I assume these recommended sizing ratios for GA aircraft take care of everything in a standard flight envelope.  I'm just asking, as I want to convert the tail volumes of the Lazair to a standard configuration as a comparison for my ultralight design which I want to design with a landing speed of 25mph,  with slats, slotted flaps and blown wings. The Lazair specs note a landing speed of 18 mph.

@Fred Use a longer tailboom to boost damping versus controllability. This will keep areas small and maintain damping. Play with the numbers until both controllability and damping look close enough to what the Lazair has.

Is this the main reason for the tail wag problems of airplanes like the V tail Bonanza?

@PeterKämpf I don't see why there would be too much controllability. I would be worried about lack of controllability, especially for multi-engine configuration. On a past project, combining OEI takeoff with even minor crosswind has been troublesome for V-Tail. On top of that, cross axis control can become nonlinear for large control deflections.

@Jimmy: Controllability has to be bought with structural strength, so there is a downside in weight. I agree about nonlinearity with large deflections in both axes at the same time.

@JohnK: Yes, and a longer fuselage would had helped. See this question for more.


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Why is the horizontal stabilizer of the Lazair swept back?
Why is the horizontal stabilizer of the Lazair swept back?
I understand the hinged elevators are perpendicular to the fuselage, but the horizontal stabilizer is actually swept back.


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What causes spiral mode instability and how do you minimize it instead of trying to dampen it?
What causes spiral mode instability in a GA plane and how do you minimize it in the first place, instead of trying to dampen it with dihedral (which is reducing efficiency by reducing vertical lift)?

One of the primary causes of spiral instability is the fact that once a turn begins, the outboard wingtip is moving along a larger circumference and therefore moving faster, and tending to produce more lift, than the inboard wingtip.  So the bank angle tends to increase.  Keeping the wingspan small will minimize this effect.  Obviously, this is a trade-off and other desirable qualities are sacrificed.
Re dihedral-- the inefficiency due to more wing area being needed to get the same amount of vertical lift component is rather minimal.  The more significant negative effects of dihedral include a excessive slip-roll coupling that creates excessive roll torque during an intentional slip (eg crosswind landing), bad effects in gusty crosswinds, poor roll response to aileron-only roll inputs, and a tendency toward "Dutch roll" yaw-roll oscillations.
Keeping the vertical fin small will help allow enough sideslip to allow whatever dihedral is present work as effectively as possible to  help minimize spiral instability, but obviously this is a trade-off as well.
For more on the relationship between sideslip and dihedral see the related answers in Is this paragraph about the dihedral effect in the FAA's Glider Flying Handbook correct? or How does the dihedral angle work? .


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Is there no warning if landing gear is not retracted during flight?
I know that most aircraft have a warning system which makes beeping sounds if an aircraft tries to land without the gear down. After reading this news article about an Air India flight 676 flying without retracting the landing gear, I was wondering if there is a reverse mechanism which warns the pilots if the landing gear is not retracted during flight?
If its not there, why?

I believed that landing gear has a speed limit and the overspeed warning would sound if you exceeded the speed ... ?

I can guarantee you, at least on 747-100/200 aircraft, that if you somehow didn't get the gear up, it would only be a matter of seconds or a minute at the most, before all 3 cockpit crew members started wondering what the hell was wrong with the aircraft. The mismatch of the crewmembers' internalized expectation of what the performance should be versus what was actually happening would be all but impossible to ignore.

Indication that it is extended, yes. Warning that it is extended (when it shouldn't be), no. Other than significant noise, drag, poor performance, high fuel consumption, etc etc tc.  That a qualified airline crew could miss this is one of those head-shaking, fouled up beyond belief, maybe time to consider finding a new career sort of moments.

I'd guess that any crew that doesn't notice the position of the gear lever, or the unusual flight characteristics of the aircraft, or the different noise it makes flying with gear extended, is also to not going to notice a warning beep/horn...

@RalphJ: This is an expected behavior from pilots of an airline which is having an $8bn debt.

I flew the light-attack, single-seat jet the A7-E while stationed aboard the Nimitz. The landing gear position indicator indicated both up-and-locked as well as down-and-locked. That doesn't mean it got much attention on the takeoff though.
I was a new pilot attached to the squadron when one of the senior JO's left for a cross-country. He was climbing to altitude when he called maintenance to discuss a problem he was having. "There seems to be something wrong with the engine," he exclaimed. Maintenance asked him what the signs were and he replied that it just wasn't generating enough thrust. "I can't seem to get above 220 KIAS, and my climb rate is very low." A series of questions followed: What is your fuel flow? Turbine outlet temperature? Altitude? Throttle position? Any unusual noises?
His answers seemed to suggest that everything appeared normal. Nothing was out of the ordinary. As we listened to the radio conversation a pilot off in the corner, with a big smile on his face, suggested he look at his lading gear position indicator.
"Hey maintenance, I found the problem. See you in a few days."
In either position, down-and-locked or up-and-locked there was no audible tone. There was just a visible indication. One was expected to follow their checklists and look at the indicator.

There is a saying "There are 2 kinds of retract pilots - those who have already landed gear up and those who are putting it off until later".
To prevent this the Piper Arrow had a system which would actually lower the gear automatically if you got into a situation that it thought was landing (low speed, low power setting) but had not yet lowered the gear. Sounds great!
The main problem with this is that in the event of an engine failure, you would be in exactly this condition; but, since gear down is EXTREMELY drag producing (that being the point behind raising gear in the first place) it would severely limit how far you can glide (cuts it by about 70%). Several people had engine failures and unintentional gear extensions and were forced to make off-airport landings as a result, when odds were good they could have made an airport if the gear had stayed up until the last minute. Turning it off immediately became an additional step in the engine failure emergency checklist, the very last place you want additional tasks.
To my knowledge the Arrow was the only plane with this system on it. Piper never tried it again. Most of the Arrows I have flown have had the system removed (which is bad because some of them did and some did not so I would be extra-stressed in an emergency to lock out the system, but might not need to).

I'm not sure how this answers the question, which is about retracting the gear, not lowering it.

Some of the comments about that incident indicated there is an illuminated light, at least in some aircraft, indicating the gear is down, but not an audible tone.

FAR §91.205 requires "Landing gear position indicator, if the aircraft has a retractable landing gear." On GA aircraft, that is either one or three lights. On mine, it is green for down and orange-yellow for up.

@JScarry the position of the landing gear lever is a pretty good indicator too :)

@jwenting If you have a Johnson bar gear lever, you can tell the position. Not so easy on my Cessna. https://www.touringmachine.com/images/Gear_Handle_Cessna210.jpg

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Why are follow-me cars used in Gran Canaria Airport in good visibility for incoming aircraft?
I've been at GCLP (Las Palmas de Gran Canaria, Spain) a few weeks ago.
I've observed that all incoming traffic was guided by a Follow Me while outgoing traffic went without one.
I was curious about that and looked for an airport chart to find more about it. The latest I've found is a Jeppesen chart from DEC 2004... so a bit outdated.
There it states in the LVP (Low Visibility Procedures) section only, that pilots have to wait at apron entry for the Follow Me while outgoing traffic should avoid requesting clearance in such a situation.
There is no notice, about what applies when LVP is not active.
What could be the reason for doing this even in good weather situations (visibility was at least 10km, if not even more)?

At a guess it’s probably a result of the accident at Tennerreif in 1977 that happened during low vis operations.


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Do French, Spanish, Italian, and Greek controllers still speak to their native pilots in their native language?
At the time of my retirement in 1999, controllers in France, Spain, Italy, and Greece typically spoke to their native pilots in their native language in spite of the fact that English was/is the international language of aviation and is specified as such by ICAO. Not following the ICAO convention deprived non-native speaking pilots of valuable situational information.
Does anyone know if any of the aforementioned countries have come around to having their controllers always speak English?

Isn't it the same in the US :-)

I do not understand why limit the scope of this question only to those 4 languages.

@Federico Of the countries I was flying into regularly, those were the only four wherein the controllers were using their native languages. In the far east, middle east, and Africa they conformed to the ICAO recommendation of the time. Russia was an exception, but that was understandable because it hadn't been long enough since the cold war had ended for the controllers to learn acceptable English.

Pilots who fly to these countries should be aware of this and try to learn some language basics

I know there was at least one incident on Avherald in Spain where they were speaking Spanish to the Spanish carriers, and English to the foreign ones, and there was a loss of situational awareness between the two.

This seems like a really bad idea. Compare, Control: "Ruritanian 2-3-5 cleared to land on runway 2-7" Pilot of ForeignAir 874, "Eek, I was about to taxi across that!" with Control: "Ruranski skrop-nop-pon voskan ploskan skrop-vin" *boom*.

Well, I just pulled up LEMD on LiveATC and heard some Spanish there. So Madrid clearly speaks Spanish sometimes, although it's probably not very busy right now (5:30 AM there). Archives from midday for LFPO and LFBD (Orly and Bordeaux) have plenty of French. Archives from midday for LGAV (Athens) approach has something definitely non-English (I can't tell if it's Greek or not, but I can't imagine anything else it'd be); LGAV has heavy use of English, but it's not exclusively English. And LiveATC has no feeds for Italy. So, for three of them the answer is definitely "yes, they still speak not-English;" for the last, LiveATC can't answer.

Greek controllers greet Greek airline pilots in Greek and the rest of the navigation communication takes place in English. Specific local information messages might also be transmitted in Greek between Greek speaking participants.

In Italy, airline traffic speaks english, but VFR/military/BAT/HEMS routinely speak both. English is mandated any time there is a non-IT speaker on frequency, otherwise IT is allowed, IIRC.

As per ICAO Annex 10PDF, it is no longer a recommendation, but a requirement that all controllers be able to speak English with an ICAO language proficiency of at least level 4. ICAO Annex 10 states:

5.2.1.2 Language to be used
5.2.1.2.1 The air-ground radiotelephony communications
  shall be conducted in the language normally used by the
  station on the ground or in the English language.
  Note 1.— The language normally used by the station on the
  ground may not necessarily be the language of the State in
  which it is located. A common language may be agreed upon
  regionally as a requirement for stations on the ground in that
  region.
  Note 2.— The level of language proficiency required for
  aeronautical radiotelephony communications is specified in
  the Appendix to Annex 1.
5.2.1.2.2 The English language shall be available, on
  request from any aircraft station, at all stations on the ground
  serving designated airports and routes used by international air
  services.
5.2.1.2.3 The languages available at a given station on the
  ground shall form part of the Aeronautical Information
  Publications and other published aeronautical information
  concerning such facilities.

This however doesn't mean that countries cannot still work with their own language and countries like France still work IFR & VFR traffic in their local langauge, whereas some countries like Germany limit German to VFR traffic and emergencies, where plain language can be used. IFR traffic in Germany is conducted in English only.

In France pilots and ATC have to speak french if they are French
This is described in the radiotelephony procedure
https://www.sia.aviation-civile.gouv.fr/dossier/texteregle/RADIOTEL_V2.pdf
section 2.4

2.4 Use of French language:
  The French language is used (except for training purposes or particular cases) between French pilot and ATC

The rules of air indicates that the ATC must be able to speak english if they have to deal with international traffic.

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